Pfizer began clinical trials of their compound, sildenafil (Viagra), on
men with erectile dysfunction. The drug proved highly effective and had few side effects. Viagra hit the market in 1998 and soon became one of the best-selling
drugs in history.

Today, Viagra and related PDE5 inhibitors tadalafil (Cialis) and vardenafil (Levitra) are some of the most financially successful
drugs on the market. The drugs are now being studied in other conditions including pulmonary hypertension, Raynaud’s syndrome (a circulatory disorder),
recovery from stroke, cystic fibrosis and as possible preventives for erectile dysfunction and heart disease.

“So we kind of accidentally
entered the Viagra field by working on cyclic AMP and cyclic GMP, which just happened to be crucial mediators (of erectile dysfunction),” says Corbin,
whose lab continues to investigate PDE5. “But we think that Viagra wouldn’t have been possible if we had not laid the groundwork and discovered the
enzyme and the mechanism.

“Our work involved some logic, some prediction, some direction, but a lot of serendipity,” he continues.
“I like to think that’s the way basic science ought to be.”